How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS AND SIGNS

Plants infected with the bacterium Xylella fastidiosa are stunted. They often have small bluish-green leaflets and fine short stems. Taproots are normal in size but when cut open, roots appear abnormally yellowish in color with dark streaks of dead tissue scattered throughout. In newly infected plants the yellowing is mostly in a ring beginning under the bark. Unlike bacterial wilt, there are no gummy pockets underneath the bark. Plants become stunted and eventually die.

COMMENTS ON THE DISEASE

Dwarf is not recognized as an economic disease of alfalfa. However, the bacterium that causes alfalfa dwarf, Xylella fastidiosa, is the same pathogen that causes Pierce's disease of grapes, a very important grape disease in California. The role that alfalfa plays in the epidemiology of Pierce's disease is important. Leafhoppers, including the blue-green sharpshooter, spread the disease from alfalfa to grapes. Increased levels of Pierce's disease in grapes located adjacent to alfalfa has been documented in the San Joaquin Valley.

MANAGEMENT

To protect grapes, minimize the attractiveness of an alfalfa stand to sharpshooters by preventing the growth of grasses. This, in turn, will reduce the transfer of the bacterial pathogen between alfalfa and grape vineyards. When possible, avoid planting alfalfa adjacent to grape vineyards in areas where Pierce's disease is prevalent.

PUBLICATION

UC IPM Pest Management Guidelines: Alfalfa
UC ANR Publication 3430
Diseases
R. M. Davis, Plant Pathology, UC Davis
C. A. Frate, UC Cooperative Extension, Tulare County

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